I just ran into a 'gotcha' that was, in retrospect, easily cured. However, it did cause me a few anxious moments.

Specifically: When upgrading from MCRS 3.18 to 3.20, you would do well to completely uninstall 3.18 first, followed by a system reboot. THEN install 3.20.

On a platform of Windows 2000 Advanced Server (SP4 and latest rollups), I ran into several bizarre 'Access Violation' errors when I simply installed 3.20 over the top of 3.18, and tried to run it. Doing the remove/fresh install trick worked perfectly.